Present embodiments relate generally to a gas turbine engine. More specifically, the present embodiments relate, but are not limited, to a radial tie-bolt support spring which increases the natural frequencies of the tie-bolt system by providing a lateral load path between the tie-bolt and the surrounding rotor structure.
A typical gas turbine engine generally possesses a forward end and an aft end with its several core or propulsion components positioned axially therebetween. An air inlet is located at a forward end of the engine. Moving toward the aft end, in order, the intake is followed by a fan, a compressor, a combustion chamber, and a turbine. It will be readily apparent from those skilled in the art that additional components may also be included in the gas turbine engine, such as, for example, low pressure and high pressure compressors, and low pressure and high pressure turbines. This, however, is not an exhaustive list.
The compressors and turbines generally include rows of airfoils that are stacked axially in stages. Each stage includes a row of circumferentially spaced stator vanes and a row of rotor blades which rotate about a high pressure or low pressure shat of the gas turbine engine. The multi-stage low pressure turbine follows the multi-stage high pressure turbine and is typically joined by the low pressure shaft to a fan disposed upstream from the low pressure compressor in a typical turbo fan aircraft engine configuration for powering an aircraft in flight.
The stator is formed by a plurality of nozzle segments which are abutted at circumferential ends to form a complete ring about the axis of the gas turbine engine. Each nozzle segment may comprise a single stator vane, commonly referred to as a singlet. Alternatively, a nozzle segment may have two stator vanes per segment, which are generally referred to as doublets. In a third embodiment, additional numbers of vanes may be disposed on a single segment. In these embodiments, the vanes extend between an inner band and an outer band.
In operation, the high pressure turbine and low pressure turbine function to maximize extraction of energy from high temperature combustion gas. The turbine section typically has a high pressure or low pressure shaft axially disposed along a center longitudinal axis of the gas turbine engine. The airfoil shaped rotor blades are circumferentially distributed on the rotor causing rotation of the internal shaft by interaction with combustion exhaust gas.
The high pressure and low pressure shafts connect to the rotor and the air compressor, such that the turbines provide rotational input to the high and low pressure air compressors respectively to drive the compressor blades. This powers the compressor during operation and subsequently drives the turbine. As the combustion gas flows downstream through the turbine stages, energy is extracted therefrom and the pressure of the combustion gas is reduced.
Some gas turbine engines utilize a tie-bolt which may extend in an axial direction through a gas turbine engine. The tie-bolt may be utilized to connect one or more compressor modules to one another and/or more turbine modules. The tie-bolt may allow the turbine modules to be removed without deconstruction of the compressor modules. Current tie-bolt systems may have various natural frequencies at which the tie-bolt may deflect laterally and whirl about the engine centerline, similar to the action of a “jump-rope”.
With current embodiments, a spanner nut may be utilized to maintain connection between an axially rearward portion of the compressor and an axial midpoint of the tie-bolt. Such spanner nut allows the compressor to maintain its assembled condition when the turbine module is removed from the gas turbine engine. The spanner nut also improves the stiffness of the tie-bolt to inhibit, or increase the natural frequency of, such “jump-rope” mode. However, the rotor structure required to employ this midpoint spanner nut is a relatively heavy component which if removed, would result in improved engine performance. While it would be desirable to reduce the weight associated with the spanner nut, removal of the spanner nut decreases the rigidity of the tie-bolt allowing increased lateral vibratory motion. Lateral motion is defined as displacement of a component or portion of a component, normally concentric with the rotor, such that the component's centerline is no longer coincident with the overall rotor centerline.
It would be desirable to improve these conditions to reduce weight of the midpoint spanner nut assembly without also decreasing the natural frequencies of the tie-bolt by not transferring lateral load of the tie-bolt.
The information included in this Background section of the specification, including any references cited herein and any description or discussion thereof, is included for technical reference purposes only and is not to be regarded subject matter by which the scope of the instant embodiments are to be bound.